The invention relates to a system for enhancing fluid flow into and through a hydrocarbon fluid production well.
Such a system is known from European patent specification 0558534 and U.S. Pat. No. 5,447,201. The system known from these prior art references comprises a series of flow control devices, in the form of adjustable valves, for controlling fluid flow from various regions of a drainhole or reservoir inflow section of the well into a production tubing within the well.
In the known system each valve throttles back production from a specific region of the drainhole section which will reduce the flux of fluids from the reservoir into that region. To compensate for the restriction of fluid flow into the well the known system is equipped with a flow booster which is installed in the production tubing downstream of the drainhole section of the well.
Disadvantages of the known system are that the downhole valves may get stuck as a result of corrosion, sand influx or deposition of salts, scale and that the combination of a series of valves and a flow booster in the well creates a large amount of wear prone components in the well and requires a complex assembly of electrical wiring to operate and control these components. Furthermore the valves can only be replaced after the flow booster in the production tubing has been removed so that replacement of valves requires a complex and costly workover operation wherein the flow booster and production tubing need to be removed to gain access to the valves.
The system according to the preamble of claim 1 is known from European patent EP 0922835, which discloses a multilateral well in which pumps are installed at the branchpoints to control the influx of the various branches into the main wellbore. The known pumps block the entrances of the branches such that maintenance or logging tools cannot be inserted into the branches and the entire production string and associated pump assemblies has to be removed from the well if maintenance or logging activities are required in one of the well branches.
U.S. Pat. No. 5,881,814 discloses another non-bypassable multistage pump assembly in a well. U.S. Pat. Nos. 3,741,298 and 5,404,943 disclose multiple pump assemblies in which the lowermost pump cannot be bypassed by logging or maintenance tools whereas the upper pump units are arranged adjacent to a by-pass conduit and are secured to the production tubing such that the entire tubing string has to be removed if the pumps need to be repaired or replaced.
The invention aims to overcome these disadvantages and to provide a flow booster systems which does not obstruct entrance to the lowermost parts of the well and where the flow boosters can be removed or replaced individually without removing the production tubing or liner.
The system according to the invention comprises a series of flow boosters comprising pump and motor assemblies which control the inflow rate of fluid from various regions of a drainhole section of a well into a production tubing or liner within the well and which flow boosters are retrievably mounted in side pockets of said production tubing or liner.
Suitably the flow boosters comprise a series of electrically or hydraulically driven moineau-type positive displacement pumps or rotary turbines which are mounted inside tubular mandrels that are retrievably mounted inside side pockets in a production liner or tubing.
Preferably each pump is equipped with sensors for measuring the flow rate and/or composition of fluids passing through the pump and the pump rate is adjustable automatically or manually in response to any significant deviation of the fluid rate and/or composition from a desired flow rate and/or composition.
It is also preferred that the production tubing extends through the drainhole section and is surrounded by an annular inflow zone and the downhole pumps are distributed along the length of said inflow zone such that each flow booster draws fluid from the inflow zone and discharges fluid into the production tubing. Suitably one or more annular insulation packets are arranged in said annular inflow zone to create an annular inflow zone in which a plurality of hydraulically insulated drainhole regions are present and a plurality of flow boosters draw fluid from a plurality of said regions. Suitable annular insulation packers are inflatable rubber packers or annular bodies of cement which are injected into the annulus at locations halfway between a pair of adjacent pumps.
It is observed that it is known from U.S. Pat. No. 3,223,109 to insert passive gas-lift valves in side pockets of a production tubing above the casing packer and above the well inflow region. The known gas-lift valves do not have an electric or hydraulic power supply and do not adjust the fluid influx into various regions of the well inflow region.